Since the beginning of the development of driving frames for electrically driven vehicles, it has been a known problem to ensure 1) adequately long possible driving distance; 2) adequately large manoeuvrability; 3) adequately low weight; 4) adequately minimum appearance; 5) adequately minimum complexity; and 6) adequate capacity to overcome obstacles. These problems have not been seen to have been solved in one invention.
A chassis constitutes a structural part or parts of an electrically driven wheelchair. Wheelchairs are often used in buildings, means of transportation and other places where there may be a limited turning space, but also outdoors where there are requirements to be able to overcome obstacles in the form of kerbstones and the like, and to drive uphill and downhill and along cross-sloping surfaces. Preferably, the wheelchair should, after an overnight recharging, work an entire day without any need for further recharging of the electrically driven wheelchair. Such electrically driven wheelchairs are today very similar within their structural groupings and may generally be divided into three different subgroups with respect to their steering: 1) Electrically driven wheelchair designed for indoor and outdoor use, normally consisting of a chassis on which two electrically driven, not steerable wheels are mounted in parallel, the steering controlled by varying the rotation speed of the individual wheels individually, and a number of supporting wheels following the direction. 2) Electrically driven wheelchair primarily designed for outdoor use and normally consisting of a chassis on which two electrically driven wheels are mounted in parallel, and one or two further supporting and steering wheels. 3) Electrically driven wheelchair primarily designed for indoor use and normally consisting of a chassis on which two or four electrically driven steering wheels are mounted.
The first subgroup can be considered a relatively simple solution, which exists in several versions. The two parallel, not steerable wheels may be configured at the front part of the chassis, the centre part of the chassis or the rear part of the chassis, supported by a number of supporting wheels, and are all associated with a number of disadvantages. They have relatively large turning radius, and the fact that they turn by regulating rotation speed of the two parallel wheels individually makes them energy inefficient since turning implies that the rotation speed of one or both of the wheels is changed. As a consequence, larger batteries are needed, which makes the wheelchair difficult to manoeuvre. The abovementioned three versions of the first category also have their own disadvantages. For example, the chassis having the two parallel, not steerable wheels placed at the rear part of the chassis may have problems driving down sloping surfaces, and the front wheels may have problems of getting stuck in loose surfaces because of surface pressure from size and weight distribution. If the two parallel, not steerable wheels are instead placed at the front part of the chassis, there is a risk of the wheelchair tilting forward when driving downwards on sloping surfaces or having problems when driving upwards on sloping surfaces.
The second subgroup includes chassis on which two electrically driven wheels are mounted in parallel, usually at the rear part of the chassis, and one or two steerable wheels at the front part of the chassis. Typically, the steerable front wheel is mechanically coupled to handlebars like on a moped, a steering rod or by means of a joystick which, by means of a control and steering system, controls a linear actuator that mechanically turns the wheels. These chassis are typically directionally stable. A known disadvantage with this chassis is the large turning radius due to the driving force in a forward direction of the vehicle, i.e. the rear wheel do not propel in the direction of the steering wheel. A further disadvantage is that if the front wheel would be turned 90° in relation to the rear wheel, the wheelchair would not drive and would risk tipping over.
The third category includes chassis on which two or four electrically driven steering wheels are mounted. In some cases the wheels may be rotated around a vertical axis mounted above the wheel. These chassis are characterized by a poor ability to climb differences in level, and increased installation height because of the rotary shaft above the driving wheel for steering, typically resulting in smaller wheels as a trade-off.
JP2009226070 describes a rear wheel driven electrically driven wheelchair in which the front wheels are free-running but steered.
EP0300185 describes a front wheel driven electrically driven wheelchair in which the rear wheels are free-running but steered.
U.S. Pat. No. 5,623,818 describes a four-wheel vehicle consisting of a front wheel set and a rear wheel set and in which the vehicle have two steering modes: the first steering mode is during normal driving where the front pair of wheels are steering wheels and the rear pair of wheels are fixed and parallel, and steering thus takes place like for a normal automobile; the second steering mode is during manoeuvring about its own axis where there is steering on both the front and the rear pair of wheels.
The abovementioned solutions seek to solve various problems concerning chassis for vehicles, but they all have problems with regard to the combination of the following aspects: driving distance, manoeuvrability, weight, size, steering complexity, and ability to climb obstacles.